As a sophomore at
Korea University in Yoon was promoted to the team's starting rotation. Yoon hurled one-run baseball over 7.1 innings and fanned 10 batters against reigning national champion
Kyungsung University in his first 2009 season game as a starter. However, Yoon was sidelined with injuries for 3 months and finished the season with a 2.36 ERA and 45 strikeouts in 34.1 innings pitched. Yoon broke out in when he racked up 6 wins as a starter and posted a 0.85 ERA in 52.2 innings pitched. He led the national collegiate league in ERA, and was sixth in strikeouts (67) and seventh in wins. During the season, Yoon was selected for the
South Korean national collegiate team and participated in the friendly baseball championship against the
United States national baseball team and the
2010 World University Baseball Championship. As a senior in , Yoon had another strong collegiate season, posting a 6–2 record and an ERA of 1.38 and fanning 66 strikeouts. At the President's Flag Championship, Yoon led his team to the championship tossing a
complete game shutout in the final game, and eventually earned the MVP honors. In September 2011, Yoon was called up to the
South Korean senior national team for the
2011 Baseball World Cup held in
Panama.
Notable international careers ==External links==